3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
User Equipment (UE) can be influenced by interference due to radio signals that are transmitted by other cells, while being served within a specific cell. The UE periodically measures a cell and reports a result of the measurement. If the UE handovers to another cell, the UE can measure a neighbor cell as well as a serving cell and report a result of the measurement. If the radio signals of other cells generate interference when measuring a specific cell, it is difficult for the UE to normally measure the specific cell. This leads to the deteriorated mobility of the UE in a wireless communication system.
In particular, if service coverage, the frequency band of a channel used, and Radio Access Technology (RAT) served by a cell are different as in a case where a macro cell, a pico cell, and a femto cell coexist, the importance of a method capable of avoiding interference caused by the cells can be further increased.
Inter-Cell Interference Coordination (ICIC) is a task of operating radio resources so that control of inter-cell interference can be maintained. An ICIC mechanism can be divided into frequency domain ICIC and time domain ICIC. ICIC includes a multi-cell Radio Resource Management (RRM) function in which pieces of information from multiple cells need to be taken into consideration.
The frequency domain ICIC coordinates the use of frequency domain resources (e.g., Resource Blocks (RBs) between multiple cells. The time domain ICIC coordinates time domain resources (e.g., subframes) between multiple cells.
In ICIC, the object that causes interference (i.e., an interfering cell) and the object that is damaged by interference (i.e., an interfered cell) are determined depending on the object on which UE performs measurement.
When UE accesses the coverage of a neighbor cell to which the UE cannot access, the UE can be subject to great interference. In order to prevent a situation in which UEs unable to access a neighbor cell cannot perform communication due to interference from the neighbor cell, the neighbor cell low-interference radio resources can be configured so that radio signals can be transmitted and received. Furthermore, measurement for the neighbor cell of UE can be subject to interference due to the radio signals of a serving cell. In order to guarantee the normal measurement of the UE for the neighbor cell, the serving cell can configure low-interference radio resources and transmit and receive radio signals.
When measuring a serving cell and a neighbor cell, UE uses low-interference radio resources configured by a cell that causes interference. This can be said to be restrictive measurement. The restrictive measurement refers to the use of a temporal section or a frequency band in which interference is avoided or reduced. The restrictive measurement can guarantee UE normal service from a serving cell to which the UE is now subscribed and can guarantee the UE smooth mobility at need.
If UE can receive service of better quality through measurement, the UE can handover to a neighbor cell. Whether UE subscribed to a source cell which has configured and operated low-interference radio resources will perform handover or not can be determined by a result of restrictive measurement. Meanwhile, the operation of the UE through the low-interference radio resources provided by the source cell may not be applied to service from a target cell during the handover or after the handover. This can deteriorate the QoS of the UE when the handover fails or after the handover. Accordingly, there is a need for a handover method through restrictive measurement that uses low-interference radio resources.